243 research outputs found
A broadband THz receiver for low background space applications
We have developed a sensitive bolometric receiver for low background space applications. In a 10 percent bandwidth at 1 THz, this receiver is approximately 100 times more sensitive than a quantum limited heterodyne receiver with a 1 GHz IF bandwidth. This receiver is designed to be used for the long wavelength band (200-700 microns) in the MIPS instrument on NASA's SIRTF satellite. The bolometers are cooled to 100 mK by an adiabatic demagnetization refrigerator. Roughly 60 g of cesium chrome alum salt is partially demagnetized to 100 mK, followed by a slow regulated downramp to compensate for the heat leak. The hold time of the ADR system is about 18 hours with a temperature stability of delta T(sub rms) approx. equals 10 micro-K. The composite bolometers have electrical responsivities of 10(exp 9)V/W and electrical NEP's of about 3x10(exp -17) W/square root of Hz. The bolometer signals are read out by JFET preamplifiers located on the helium plate and operated at 120 K. We have addressed a number of space qualification issues, such as the development of an analog magnet controller, construction of a cryogenic shake-table for bolometers and selection of the paramagnetic salt CCA which can survive a bakeout at 50 C. The receiver is scheduled to be flown in the spring of 1992 on a balloon telescope. This flight has a dual purpose. One is to provide realistic test of the capabilities of the new receiver. The other is to search for anisotropies in the cosmic microwave background on scales of a few degrees
COMPASS: a 2.6m telescope for CMBR polarization studies
COMPASS (COsmic Microwave Polarization at Small Scale) is an experiment devoted to measuring the polarization of the CMBR. Its design and characteristics are presented
Design, Fabrication, and Testing of Lumped Element Kinetic inductance Detectors for 3 mm CMB Observations
Kinetic inductance detectors (KIDs) are a promising technology for low-noise, highly-multiplexible mm- and submm-wave detection. KIDs have a number of advantages over other detector technologies, which make them an appealing option in the cosmic microwave background B-mode anisotropy search, including passive frequency domain multiplexing and relatively simple fabrication, but have suffered from challenges associated with noise control. Here we describe design and fabrication of a 20-pixel prototype array of lumped element molybdenum KIDs. We show Q, frequency and temperature measurements from the array under dark conditions. We also present evidence for a double superconducting gap in molybdenum
The Spectrum of Integrated Millimeter Flux of the Magellanic Clouds and 30-Doradus from TopHat and DIRBE Data
We present measurements of the integrated flux relative to the local
background of the Large and Small Magellanic Clouds and the region 30-Doradus
(the Tarantula Nebula) in the LMC in four frequency bands centered at 245, 400,
460, and 630 GHz, based on observations made with the TopHat telescope. We
combine these observations with the corresponding measurements for the DIRBE
bands 8, 9, and 10 to cover the frequency range 245 - 3000 GHz (100 - 1220
micrometers) for these objects. We present spectra for all three objects and
fit these spectra to a single-component greybody emission model and report
best-fit dust temperatures, optical depths, and emissivity power-law indices,
and we compare these results with other measurements in these regions and
elsewhere. Using published dust grain opacities, we estimate the mass of the
measured dust component in the three regions.Comment: 41 pages, 4 figures. Accepted for publication in Astrophysical
Journa
Lack of clustering in low-redshift 21-cm intensity maps cross-correlated with 2dF galaxy densities
We report results from 21-cm intensity maps acquired from the Parkes radio
telescope and cross-correlated with galaxy maps from the 2dF galaxy survey. The
data span the redshift range and cover approximately 1,300
square degrees over two long fields. Cross correlation is detected at a
significance of . The amplitude of the cross-power spectrum is low
relative to the expected dark matter power spectrum, assuming a neutral
hydrogen (HI) bias and mass density equal to measurements from the ALFALFA
survey. The decrement is pronounced and statistically significant at small
scales. At , the cross power spectrum is more
than a factor of 6 lower than expected, with a significance of .
This decrement indicates either a lack of clustering of neutral hydrogen (HI),
a small correlation coefficient between optical galaxies and HI, or some
combination of the two. Separating 2dF into red and blue galaxies, we find that
red galaxies are much more weakly correlated with HI on scales, suggesting that HI is more associated with blue
star-forming galaxies and tends to avoid red galaxies.Comment: 12 pages, 3 figures; fixed typo in meta-data title and paper author
Measurements of Anisotropy in the Cosmic Microwave Background Radiation at 0.5 Degree Angular Scales Near the Star Gamma Ursae Minoris
We present results from a four frequency observation of a 6 x 0.6 degree
strip of the sky centered near the star Gamma Ursae Minoris during the fourth
flight of the Millimeter-wave Anisotropy eXperiment (MAX). The observation was
made with a 1.4 degree peak-to-peak sinusoidal chop in all bands. The FWHM beam
sizes were 0.55 +/- 0.05 degrees at 3.5 cm-1 and 0.75 +/-0.05 degrees at 6, 9,
and 14 cm-1. During this observation significant correlated structure was
observed at 3.5, 6 and 9 cm-1 with amplitudes similar to those observed in the
GUM region during the second and third flights of MAX. The frequency spectrum
is consistent with CMB and inconsistent with thermal emission from interstellar
dust. The extrapolated amplitudes of synchrotron and free-free emission are too
small to account for the amplitude of the observed structure. If all of the
structure is attributed to CMB anisotropy with a Gaussian autocorrelation
function and a coherence angle of 25', then the most probable values of
DeltaT/TCMB in the 3.5, 6, and 9 cm-1 bands are 4.3 (+2.7, -1.6) x 10-5, 2.8
(+4.3, -1.1) x 10-5, and 3.5 (+3.0, -1.6) x 10-5 (95% confidence upper and
lower limits), respectively.Comment: 16 pages, postscrip
Measurements of Anisotropy in the Cosmic Microwave Background Radiation at Degree Angular Scales Near the Stars Sigma Hercules and Iota Draconis
We present results from two four-frequency observations centered near the
stars Sigma Hercules and Iota Draconis during the fourth flight of the
Millimeter-wave Anisotropy eXperiment (MAX). The observations were made of 6 x
0.6-degree strips of the sky with 1.4-degree peak to peak sinusoidal chop in
all bands. The FWHM beam sizes were 0.55+/-0.05 degrees at 3.5 cm-1 and a
0.75+/-0.05 degrees at 6, 9, and 14 cm-1. Significant correlated structures
were observed at 3.5, 6 and 9 cm-1. The spectra of these signals are
inconsistent with thermal emission from known interstellar dust populations.
The extrapolated amplitudes of synchrotron and free-free emission are too small
to account for the amplitude of the observed structures. If the observed
structures are attributed to CMB anisotropy with a Gaussian autocorrelation
function and a coherence angle of 25', then the most probable values are
DT/TCMB = (3.1 +1.7-1.3) x 10^-5 for the Sigma Hercules scan, and DT/TCMB =
(3.3 +/- 1.1) x 10^-5 for the Iota Draconis scan (95% confidence upper and
lower limits). Finally a comparison of all six MAX scans is presented.Comment: 13 pages, postscript file, 2 figure
Complex Visibilities of Cosmic Microwave Background Anisotropies
We study the complex visibilities of the cosmic microwave background
anisotropies that are observables in interferometric observations of the cosmic
microwave background, using the multipole expansion methods commonly adopted in
analyzing single-dish experiments. This allows us to recover the properties of
the visibilities that is obscured in the flat-sky approximation. Discussions of
the window function, multipole resolution, instrumental noise, pixelization,
and polarization are given.Comment: 22 pages, 1 figure include
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